1. Field of the Invention
The present invention relates to an apparatus for supplying granular or pulverous thermoplastic and/or duroplastic materials and/or rubber and/or similar materials to a processing or treating machine, for example an extruder, according to which the apparatus has a charging hopper with conduit-like devices for drawing off the gases which are released from the material.
The term "plastic material" as used in this specification and in the claims refers to all suitable thermoplastic and duroplastic materials, to rubber, and to equivalent materials. For the sake of simplicity, the term "plastic material" will be used to cover all these materials.
2. Description of the Prior Art
From the U.S. Pat. No. 3,489,830 (Grigull), an apparatus of the above mentioned type is known through which plastic material is supplied to an extruder. With this heretofore known apparatus, the material passes through two hoppers, which are arranged one above the other, prior to the material passing out of the outlet of the lower hopper into a conveying screw which conveys the material to the extruder. A vacuum exists in these two hoppers, whereby a degasification of the plastic raw material is achieved; the material is freed of monomerous residual constituents, oxygen, water vapor, and other gases. If these gases are not withdrawn, the extruded product contains gas occlusions, imperfections in the chemical structure, and/or similar flaws. Since the gas particles which are to be withdrawn are essentially formed in the vicinity of the conveying screw because the material in that area has a higher temperature, the heretofore known apparatus is equipped within the lower hopper with one or more conduits or a conduit-like lining which withdraws the gas only a few millimeters above the conveying screw and guides the gas upwardly through the hopper to relatively close beneath the top of the hopper, where the greatest vacuum or underpressure exists.
Such an arrangement has the drawback that those gas particles which are not withdrawn at the conveying screw rise in the hopper under the influence of the vacuum and thus pass through all of the material which is present in the hopper. In this connection, these gas particles are even enriched by those gas particles which are themselves released in the hopper. Despite the withdrawal at the outlet of the hopper, quantities of gas can thus pass through the hopper and the material present therein up to the top, resulting in an undesired condensation which can only be removed with difficulty. During the operation, even a constant increasing concentration of the undesired gases occurs in the plastic material, so that eventually a final withdrawal of the condensates which wet the material to an excessive extent is no longer possible.